Support-bearing copper foil comprising a support metal layer, a release layer and a thin copper layer has been used in the production of ultra high density printed wiring boards. After the support-bearinq copper foil is laminated with a resin base material with the thin copper layer facing the resin base material and molded together, the support metal layer is peeled off, and the thin copper layer is then etching processed to form a circuit. As compared with methods using common copper foil having no support metal layer, this method is advantageous to form fine circuits because the thin copper layer may be formed thinner than the common copper foil.
Conventional release layers containing benzotriazole type organic compounds or inorganic compounds such as chromium oxide allow copper diffusing into the release layers at high temperatures, and make it difficult to peel off the release layers from support metal layers. It therefore has been proposed to provide the support metal layer or the thin copper layer with a layer that faces the release layer and prevents the diffusion of copper (for example, see Patent Document 1).
The above-described method successively prevents the diffusion of copper and suppresses the increase of peeling strength at high temperatures. However, due to the complicated layer structure and the interfacial destruction owing probably to difference in coefficient of thermal expansion or changes in crystal structures, the support metal layer spontaneously peels off from the thin copper layer. This results in a bad influence upon the workability and quality of copper clad laminates, such as the oxidative deterioration of the surface of the thin copper layer by exposure to hot air, or damage during cutting processing.
Patent Document 1: JP 2002-292788 A